Bitwarden Mobile: https://github.com/bitwarden/mobile

I will freely admit I am strongly biased against Xamarin as there are so few cases where I think it's unequivocally the right choice, and Bitwarden isn't one of them. It would make more sense to take the work done in their desktop electron app and use that as part of an Ionic hybrid mobile app than to screw around with the layercake of bugs and mismatched APIs that Xamarin is. Moreover, since this is a serious app from a security point of view it really should go full vendor native IMO.